ESSENTIALS OF DIAGNOSIS
Important to identify specific fibrosing disorders.
Idiopathic disease may require biopsy for diagnosis.
Accurate diagnosis identifies patients most likely to benefit from therapy.
The most common diagnosis among patients with diffuse interstitial lung disease is one of the interstitial pneumonias, including all the entities described in Table 9–17. Historically, a diagnosis of interstitial lung disease was based on clinical and radiographic criteria with only a small number of patients undergoing surgical lung biopsy. When biopsies were obtained, the common element of fibrosis led to the grouping together of several histologic patterns under the category of interstitial pneumonia or idiopathic pulmonary fibrosis (IPF). Distinct histopathologic features are now understood to represent different natural histories and responses to therapy (Table 9–17). Therefore, in the evaluation of patients with diffuse interstitial lung disease, clinicians should attempt to identify specific disorders.
Table 9–17.Idiopathic interstitial pneumonias. ||Download (.pdf) Table 9–17. Idiopathic interstitial pneumonias.
|Name and Clinical Presentation ||Histopathology ||Radiographic Pattern ||Response to Therapy and Prognosis |
Usual interstitial pneumonia (UIP)
Age 55–60, slight male predominance. Insidious dry cough and dyspnea lasting months to years. Clubbing present at diagnosis in 25–50%. Diffuse fine late inspiratory crackles on lung auscultation. Restrictive ventilatory defect and reduced diffusing capacity on pulmonary function tests. ANA and RF positive in ∼25% in the absence of documented collagen-vascular disease.
|Patchy, temporally and geographically nonuniform distribution of fibrosis, honeycomb change, and normal lung. Type I pneumocytes are lost, and there is proliferation of alveolar type II cells. “Fibroblast foci” of actively proliferating fibroblasts and myofibroblasts. Inflammation is generally mild and consists of small lymphocytes. Intra-alveolar macrophage accumulation is present but is not a prominent feature. ||Diminished lung volume. Increased linear or reticular bibasilar and subpleural opacities. Unilateral disease is rare. High-resolution CT scanning shows minimal ground-glass and variable honeycomb change. Areas of normal lung may be adjacent to areas of advanced fibrosis. Between 2% and 10% have normal chest radiographs and high-resolution CT scans on diagnosis. ||No randomized study has demonstrated improved survival compared with untreated patients. Inexorably progressive. Median survival approximately 3 years, depending on stage at presentation. Nintedanib and pirfenidone reduce rate of decline in lung function. |
Respiratory bronchiolitis-associated interstitial lung disease (RB-ILD)1
Age 40–45. Presentation similar to that of UIP though in younger patients. Similar results on pulmonary function tests, but less severe abnormalities. Patients with respiratory bronchiolitis are invariably heavy smokers.
|Increased numbers of macrophages evenly dispersed within the alveolar spaces. Rare fibroblast foci, little fibrosis, minimal honeycomb change. In RB-ILD the accumulation of macrophages is localized within the peribronchiolar air spaces; in DIP1, it is diffuse. Alveolar architecture is preserved. ||May be indistinguishable from UIP. More often presents with a nodular or reticulonodular pattern. Honeycombing rare. High-resolution CT more likely to reveal diffuse ground-glass opacities and upper lobe emphysema. ||Spontaneous remission occurs in up to 20% ...|